Rheology modifier

Abstract

The present invention relates to a process for preparing hydrophobically modified alkylene oxide polyurethanes by polymerizing, in the presence of a catalyst, a solvent-free melt of a polyisocyanate branching agent; a water-soluble polyalkylene glycol having an M w of from 2000 to 11,000 Daltons; and a diisocyanate; wherein the solvent-free melt further includes a hydrophobic capping agent, or a hydrophobic capping agent is added to the melt after the addition of catalyst. Hydrophobically modified alkylene oxide polyurethanes prepared by the process of the present invention show excellent ICI/KU properties and are useful as thickeners for coatings formulations.

The invention claimed is: 
     
       1. A process comprising contacting a solvent-free melt of a polyisocyanate branching agent; a water-soluble polyalkylene glycol having an M w  of from 2000 to 11,000 Daltons; and a diisocyanate with a polymerization promoting catalyst under conditions sufficient to form a hydrophobically modified alkylene oxide urethane polymer; with the proviso that either: 1) the solvent-free melt further includes a hydrophobic capping agent prior to contact of the melt with the catalyst; or 2) a hydrophobic capping agent is added to the melt after contact of the melt with the catalyst;
 wherein the molar equivalent ratio of glycol to polyisocyanate branching agent is from 4 to 20; and the molar equivalent ratio of total isocyanate groups from the polyisocyanate branching agent and the diisocyanate to glycol hydroxyl groups is 1.1 to 1.6; and wherein the hydrophobic capping agent is an alcohol or an alkoxylate thereof, an amine or an alkoxylate thereof, or a tertiary aminoalcohol or an alkoxlyate thereof. 
 
     
     
       2. The process of  claim 1  wherein the solvent-free melt further comprises a hydrophobic capping agent prior to contact of the melt with the catalyst; the process is carried out at a temperature in the range of 70° C. to 120° C.; the water-soluble polyalkylene glycol is a polyethylene glycol having M w  of from 4000 to 10,000 Daltons; and the catalyst is a bismuth catalyst; wherein the hydrophobic capping agent is a C 6 -C 18 -alcohol or a C 6 -C 18  tertiary aminoalcohol. 
     
     
       3. The process of  claim 2  wherein the process is carried out at a temperature in the range of 85° C. to 115° C.; the polyisocyanate branching agent is hexamethylene diisocyanate isocyanurate; isophorone diisocyanate isocyanurate; tris(isocyanatohexyl)biuret; 1,6,11-undecane triisocyanate, or the reaction product of a diisocyanate and a polyol branching agent; the hydrophobic capping agent comprises at least one of n-octanol, n-nonanol, n-decanol, n-undecanol, n-dodecanol, 2-ethylhexanol, 2-butyl-1-octanol, or 3,7-dimethyl-1-octanol; and the catalyst is bismuth octoate;
 wherein the molar equivalent ratio of hydroxyl groups in the glycol to isocyanate groups in the polyisocyanate branching agent is from 6 to 15; and the molar equivalent ratio of total isocyanate groups to glycol hydroxyl groups is 1.2 to 1.4. 
 
     
     
       4. The process of  claim 3  wherein the polyisocyanate branching agent is hexamethylene diisocyanate isocyanurate, isophorone diisocyanate isocyanurate, or the reaction product of a diisocyanate and a glycerol ethoxylate, which reaction product has the following formula: 
       
         
           
           
               
               
           
         
         where each R 1  is independently a divalent C 4 -C 20  linear, branched, or cycloaliphatic group, or a combination thereof; and x+y+z is in the range of 0 to 200. 
       
     
     
       5. The process of  claim 1  wherein the hydrophobic capping agent is a C 6 -C 18  alcohol which is added to the melt after contact of the melt with the catalyst; the process is carried out at a temperature in the range of 70° C. to 120° C.; the water-soluble polyalkylene glycol is a polyethylene glycol having M w  of from 4000 to 10,000 Daltons; and the catalyst is a tertiary amine or a tin, bismuth, or zinc catalyst. 
     
     
       6. The process of  claim 5  wherein the process is carried out at a temperature in the range of 85° C. to 115° C.; the polyisocyanate branching agent is hexamethylene diisocyanate isocyanurate; isophorone diisocyanate isocyanurate; tris(isocyanatohexyl)biuret; 1,6,11-undecane triisocyanate, or the reaction product of a diisocyanate and a polyol branching agent; the C 6 -C 18  alcohol comprises at least one of n-octanol, n-nonanol, n-decanol, n-undecanol, n-dodecanol, 2-ethylhexanol, 2-butyl-1-octanol, or 3,7-dimethyl-1-octanol; and the catalyst is bismuth octoate;
 wherein the molar equivalent ratio of glycol to polyisocyanate branching agent is from 6 to 15; and the molar equivalent ratio of total isocyanate groups to glycol hydroxyl groups is 1.2 to 1.4. 
 
     
     
       7. The process of  claim 6  wherein polyisocyanate branching agent is hexamethylene diisocyanate isocyanurate, isophorone diisocyanate isocyanurate, or the reaction product of a diisocyanate and a glycerol ethoxylate, which reaction product has the following formula: 
       
         
           
           
               
               
           
         
         where each R 1  is independently a divalent C 4 -C 20  linear, branched, or cycloaliphatic group, or a combination thereof; and x+y+z is in the range of 0 to 200. 
       
     
     
       8. The process of  claim 2  wherein the C 6 -C 18  tertiary amino alcohol is a reaction product of a diamylamine and a butyl glycidyl ether; and the catalyst is bismuth octoate. 
     
     
       9. A composition comprising a binder, a pigment, and a hydrophobically modified alkylene oxide urethane polymer prepared by the process of  claim 1 .